# CBSE Guess paper class XII Physics 2008 3

Guess Paper – 2008

Class – XII

Subject - Physics

( Based on the new pattern of CBSE board examination 2009 )

ELECTROSTATICS

( NCERT units 1 and 2 )

Time Allowed : 3 hours Maximum Marks : 70

(a) All questions are compulsory

(b) Question numbers 1 to 8 are very short answer type questions, carrying one mark each.

(c) Question numbers 9 to 18 are short answer type questions, carrying two marks each.

(d) Question numbers 19 to 27 carry three marks each.

(e) Question numbers 28 to 30 are long answer type questions, carrying five marks each.

(f) Use of calculators is not permitted. However, you may use log tables, if necessary.

Q.1> How many protons will have the total charge of 1C

Q.2> What is the dielectric constant of Silver?

Q.3> Find the electric field b/w 2 metal plates 5mm apart, connected by a 12V battery.

Q.4> Write the value of Coulomb constant ( K ) and mention its units.

Q.5> Find the work done in placing a charge of 8nC on a condenser of capacity 100micro-farad.

Q.6> Define equipotential surface and draw EPS for a single point charge.

Q.7> What is the angle b/w electric dipole moment and the electric field on its equatorial point?

Q.8> Sketch electric field lines for a dipole.

Q.9> The electrostatic force on a small sphere of charge 4C due to another small sphere of charge 8C in air is F. What is the distance b/w the 2 spheres. What is the force on the –8C sphere due to the first sphere. What will the force be if the spheres are dipped in a liquid having dielectric constant K

Q.10> An electron is placed inside a capacitor ( 5μf ). It is found to be stationary i.e. its weight is

balanced by the electrostatic force. Find the potential difference across the plates of the capacitor if the plate area is A.

Q.11> Equal charges each of 1C are placed at x = 0, 2 , 4 , 8 , 16 cm. Find the force experienced by the charge at x=2 cm. Define electric field intensity at x=2 and find it.

Q.12> What is the work done in moving a charge 100nC from point A to point B 5cms apart, where both points A and B lie on the same equipotential surface? Explain your answer.

Q.13> Define electric flux. Is it a vector quantity. Give its units. If the flux entering and leaving a closed surface is Φ1 and Φ2 find the charge inside that surface.

Q.14> Define electric potential. What is line integral of electric field over a closed loop?

# Q.16> A uniform electric field E exists b/w the 2 charged plates as shown in the

figure. What would be the work done in moving a charge q along the path A B

ABCDA. Hence define conservative fields and give 2 properties.

Q.17> Write 2 differences b/w charge and mass.

Q.18> Calculate the potential at the center of a square of side 1.414m, which

carries at its 4 corner charges of 2nC , 1nC , -2nC , -3nC respectively.

Q.19> Two point charges 4q and q are fixed a distance 2m apart. Find the point on the line joining them at which the net electric field intensity in zero. What is the potential at this point. If a charge of magnitude –3q is placed at this point, in which direction will it move. What will be its potential energy at this point?

# Q.20> Charges of 4μC each are placed at the four corners of a

square of side 1m. Find the electric field and potential at the center. Q1

What would these quantities be if one of the given charges were negative? 4m

Q.21> Three charges –Q1 , +Q2 , -Q3 are placed as shown in the 3m

figure. Find in vector form the force acting on Q2 charge. Q2 -Q3

# Each capacitor is of 1μfarad

Q.24> A hollow sphere of radius R is given a charge Q. On a graph plot the variation of Electric field intensity versus distance from center. On another graph plot the potential against distance.

Q.25> Two point electric charges A and B of unknown magnitude and sign are placed d distance apart. The electric field is zero at a point, not b/w the charges but on the line joining them and closer to A. Write 2 essential conditions for this to happen

Q.26> Explain dielectric polarization. A certain region of space is to be protected from external electric field. Suggest a suitable method.

Q.27> What are electric field lines? Give 4 properties and define neutral point.

Q.28> Define capacitance and give its units. Explain the principle of a parallel plate capacitor and the use of earthing. Derive the formula for capacitance of a parallel plate capacitor with a slab.

Q.29> State Gauss’s theorem. Give its mathematical expression. Derive an expression for the electric field intensity at any point due to an infinite plane sheet of charge of density σ C/m2

Q.30> Using a proper figure, explain the construction and working of a VanDeGraff generator.

OR

Q.30>( choice 2 ) Use Gauss’s law to obtain an expression for the electric field due to an infinitely long straight uniformly charged wire.

(b) Electric field in the given figure is directed along + X direction and given by

Ex = 5Ax + 2B, where E is in NC-1 and A = 10 and B = 5 in SI units. x is in metre.

calculate.

(i) the electric flux through the cube.

ii) net charge enclosed within the cube.

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